At present, due to the environmental pollution of fuel-powered vehicles and the continuous hike of international oil price, pure electric vehicle (PEV) as a branch of green new energy technology has such advantages as zero emission, low noise, simple structure and realization of diversified transport energy and gradually attracts people's attraction and its market share increases year by year. Nonetheless, PEV still has much to be desired. The driving mechanism for PEV at present still adopts the motor+gearbox model, but the gearbox has the defects of complex structure, difficult assembly, large weight and high manufacturing cost and greatly increases the production cost of the vehicle. Further, due to limited electric quantity of batteries and limited power of motors, conventional PEV also has the outstanding drawbacks of short mileage and poor power performance, which have become main bottlenecks to the popularization of PEV.